After the user submits a form for processing, it is possible for the user to inadvertently hit the back button and resubmit the form again.Â It is possible to prevent this possibility if necessary. The strategy involves the use of a timestamp that is saved in the session as well as embedded on the form. When the form is submitted for processing, the timestamp in the form is compared to the value saved in the session. If the timestamps do not match, it is assumed that either the form has expired or has been submitted.